Cutting fluid, cutting method, and smoothness improver for cut surface

ABSTRACT

A cutting fluid comprising a sugar solution containing any sugar alcohol selected from among sorbitol, reduced starch syrup and reduced maltose syrup and having a viscosity of 9.7 mPa·s or more. According to the present invention, the cut surface can have improved smoothness and, hence, the polishing step which has conventionally been conducted after cutting can be shortened, simplified, or omitted to greatly contribute to an improvement in working efficiency. Furthermore, since chipping can be diminished, the present invention can greatly contribute to an improvement in the precision of the shape or dimensions of works or to an improvement in yield.

TECHNICAL FIELD

The present invention relates to a cutting fluid, a cutting method, and a smoothness improver for a cut surface. Specifically, the present invention relates to a cutting fluid and a smoothness improver for a cut surface which can improve the smoothness of a cut surface of a workpiece material and reduce the chipping of the workpiece material during cutting, and a cutting method using the cutting fluid.

BACKGROUND ART

Cutting fluids are generally used in order to achieve improvement in machining accuracy, improvement in the surface texture of works, efficient cutting, prolongation of tool life, etc. by effects such as reduction in friction during cutting, cooling of heat generated by cutting, and washing of scraps. The cutting fluids are broadly classified into water-insoluble and water-soluble ones and include various types. For example, petroleum-derived ethylene glycol or propylene glycol, or a water-soluble cutting fluid with any of these polymers as a base material has heretofore been used in cutting difficult-to-cut hard brittle ingot such as silicon for semiconductors, ceramic or glass in high industrial demand using a wire saw.

However, the cutting fluid with an ethylene glycol or propylene glycol substance as a base material presents the following problems (i) to (iv):

(i) a cutting process using a wire saw with an abrasive fixed thereon (fixed abrasive machining) produces the poor smoothness of a cut surface of a workpiece material,

(ii) chipping occurs,

(iii) a cutting process using a wire saw with an abrasive unfixed thereon and a cutting fluid containing an abrasive dispersed therein (loose abrasive machining) has poor sedimentation properties of the abrasive in the cutting fluid and has the difficulty in recovering the abrasive from the cutting fluid after use, and

(iv) safety to human bodies is of concern about a petroleum-derived component contained in the cutting fluid.

Accordingly, various cutting fluids have been researched and developed in order to solve these problems. For example, Patent Literature 1 discloses an aqueous cutting fluid comprising an abrasive dispersed in an aqueous fluid containing an auxiliary agent composed mainly of a food additive, and an emulsifier for food. Patent Literature 2 discloses a cutting fluid for silicon ingot slicing containing an organic reducing agent and water and having a pH of 4.0 to 8.0.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2001-164240

Patent Literature 2: Japanese Patent Laid-Open No. 2012-253105

SUMMARY OF INVENTION Technical Problem

Although the aqueous cutting fluid described in Patent Literature 1 solves the safety problem of (iv) and the cutting fluid for silicon ingot slicing described in Patent Literature 2 solves the smoothness problem of (i), neither of these literatures discusses the chipping problem of (ii) and the abrasive recovery property problem of (iii) or solves these problems. Thus, there has been a demand for the development of a cutting fluid that contributes to the solution of the above problems (i) to (iv).

The present invention has been made in order to solve these problems. An object of the present invention is to provide a cutting fluid and a smoothness improver for a cut surface which improve the smoothness of a cut surface of a workpiece material (hereinafter, referred to as a “cut surface”), reduce chipping, facilitate recovering an abrasive, and decrease safety concerns to human bodies, and a cutting method using the cutting fluid.

Solution to Problem

The present inventors have conducted diligent studies and consequently found that use of a sugar solution containing any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup and having a viscosity of 9.7 mPa·s or more, as a cutting fluid can improve the smoothness of a cut surface and reduce chipping. Accordingly, each of the following aspects of the invention has been completed on the basis of these findings.

(1) The cutting fluid according to the present invention comprises a sugar solution containing any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup and having a viscosity of 9.7 mPa·s or more.

(2) The cutting fluid according to the present invention can be used in fixed abrasive machining with a wire saw.

(3) The cutting method according to the present invention has a step of cutting a workpiece material using, as a cutting fluid, a sugar solution containing any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup and having a viscosity of 9.7 mPa·s or more.

(4) In the cutting method according to the present invention, the process of cutting work can be fixed abrasive machining with a wire saw.

(5) The smoothness improver for a cut surface according to the present invention comprises any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup as an active ingredient.

Advantageous Effects of Invention

According to the present invention, the smoothness of a cut surface can be improved. This leads to shortening, simplification or omission of a polishing step which is performed after conventional cutting and can make a great contribution to improvement in work efficiency.

According to the present invention, chipping can be reduced. This can make a great contribution to improvement in the shape or dimension accuracy of works and improvement in yield.

A sugar solution having a viscosity of 9.7 mPa·s or more is moderately viscous and permits favorable dispersion of an abrasive, while this sugar solution can be centrifuged to sediment the abrasive rapidly and conveniently. Thus, according to the present invention, the abrasive can be easily recovered from the cutting fluid after use.

As is evident from the fact that sorbitol, reduced starch syrup and reduced maltose syrup are used as food or a food additive, these substances are safe to human bodies. Thus, according to the present invention, safety concerns to human bodies associated with use of the cutting fluid can be remarkably decreased. This can make a great contribution to improvement in working environment during cutting and reduction in environmental load during liquid waste disposal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing the structure of a cutting machine (rocking vibration-assisted diamond wire saw) used in the present Examples.

FIG. 2 is a schematic diagram showing the measurement range of a brittle fracture area of a wafer fabricated in the present Examples.

FIG. 3 is a schematic diagram showing those to which “chipping depth” and “chipping width” of a wafer fabricated in the present Examples refer.

FIG. 4 is a schematic diagram showing the measurement range of surface waviness of a wafer fabricated in the present Examples.

FIG. 5 Upper figures of FIG. 5 show photographs of cut surfaces of wafers fabricated using a commercially available cutting fluid or a sugar solution of sorbitol, and scores related to smoothness. Bottom figures of FIG. 5 show magnified photographs of the cut surfaces.

FIG. 6 shows brittle fracture areas in cut surfaces of wafers fabricated using a commercially available cutting fluid or a sugar solution of sorbitol.

FIG. 7 shows means of chipping depth and chipping width of wafers fabricated using a commercially available cutting fluid or a sugar solution of sorbitol, and scores thereof.

FIG. 8 shows photographs showing cut surfaces of wafers fabricated using a commercially available cutting fluid or a sugar solution of each of various sugar alcohols, and scores related to smoothness.

FIG. 9 shows means of chipping depth and chipping width of wafers fabricated using a commercially available cutting fluid or a sugar solution of each of various sugar alcohols, and scores thereof.

FIG. 10 shows photographs of cut surfaces of wafers fabricated using a commercially available cutting fluid or a sugar solution of each of various sugar alcohols differing in viscosity, and scores related to smoothness.

FIG. 11 shows means of chipping depth and chipping width of wafers fabricated using a commercially available cutting fluid or a sugar solution of each of sorbitols differing in viscosity, and scores thereof.

FIG. 12 shows largest cross-sectional heights (Wt) in waviness curve of wafers fabricated using a sugar solution of each of sorbitols differing in viscosity.

FIG. 13 shows photograph showing a cut surface of a silicon wafer fabricated using a sugar solution of sorbitol as a cutting fluid.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the cutting fluid, the cutting method, and the smoothness improver for a cut surface according to the present invention will be described in detail.

The cutting fluid according to the present invention comprises a sugar solution containing any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup and having a viscosity of 9.7 mPa·s or more.

The cutting method according to the present invention has the step of cutting a workpiece material using the cutting fluid according to the present invention.

The smoothness improver for a cut surface according to the present invention comprises any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup as an active ingredient.

The cutting fluid and the smoothness improver for a cut surface according to the present invention may contain any one type of sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup or may contain two or more types of sugar alcohols selected therefrom.

The sorbitol is a sugar alcohol that is obtained by converting an aldehyde group of glucose to a hydroxy group.

The reduced starch syrup is a sugar alcohol that is obtained by reducing starch syrup. The starch syrup is obtained by saccharifying starch with an acid, an enzyme, or the like and is a mixture of glucose, an oligosaccharide such as maltose and a polysaccharide such as dextrin. Accordingly, the reduced starch syrup is also a mixture containing two or more sugar alcohols among monosaccharide alcohol (sorbitol), disaccharide alcohol (maltitol), trisaccharide alcohol and tetrasaccharide or higher polysaccharide alcohol.

The reduced starch syrup may be divided, according to the degree of saccharification, into highly saccharified reduced starch syrup (containing 30 to 50% by mass of monosaccharide alcohol, 20 to 50% by mass of disaccharide alcohol, and 25% by mass or less of trisaccharide or higher sugar alcohol when the total mass of the sugar is defined as 100%), moderately saccharified reduced starch syrup (containing less than 30% by mass of monosaccharide alcohol and less than 50% by mass of pentasaccharide or higher sugar alcohol when the total mass of the sugar is defined as 100%) and low saccharified reduced starch syrup (containing 50% by mass or more of pentasaccharide or higher sugar alcohol when the total mass of the sugar is defined as 100%). In the present invention, any of these reduced starch syrups can be used. Reduced starch syrup designated as so-called “sorbitol preparation”, which contains 50% by mass or more of monosaccharide alcohol (sorbitol), can also be used.

The reduced maltose syrup is a sugar alcohol that is obtained by reducing maltose syrup. The maltose syrup is starch syrup composed mainly of maltose and also contains glucose, dextrin, or the like in addition to maltose. Accordingly, the reduced maltose syrup is also a mixture composed mainly of reduced maltose (maltitol), but also containing one or more sugar alcohols among monosaccharide alcohol (sorbitol), trisaccharide alcohol and tetrasaccharide or higher polysaccharide alcohol.

Hereinafter, any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup is referred to as the “present sugar alcohol”. In the present invention, a commercially available product may be used directly as the present sugar alcohol, or the present sugar alcohol used may be produced according to a method known to those skilled in the art. Examples of the known method for producing the present sugar alcohol can include reduction reaction of hydrogenating a reducible raw sugar. Specifically, sorbitol can be produced through reduction reaction with glucose as a raw sugar; reduced starch syrup can be produced through reduction reaction with starch syrup as a raw sugar; and reduced maltose syrup can be produced by reduction with maltose syrup as a raw sugar.

The reduction reaction by hydrogenation can be performed, for example, by charging a high-pressure reactor with an aqueous solution of 40 to 75% by mass of a raw sugar together with a reduction catalyst, setting the hydrogen pressure to 4.9 to 19.6 MPa and the reaction solution temperature to 70 to 180° C. in the reactor, and performing reaction with mixing and stirring until hydrogen absorption is no longer observed. Then, the reduction catalyst is separated, and the residue can be decolorized and desalted by ion-exchange resin treatment and, if necessary, activated carbon treatment or the like and then concentrated into a predetermined concentration to make a high-concentration sugar alcohol solution.

More specifically, for sorbitol, as described in, for example, Japanese Patent Laid-Open No. 7-145090, an electromagnetic stirring-type autoclave having an internal capacity of 550 mL is charged with 150 g of aqueous crystalline glucose, 125 g of water, and 5 g of a Raney nickel catalyst, followed by reduction reaction at 130° C. for 2 hours at a hydrogen pressure kept at 12.75 MPa. Subsequently, the Raney nickel catalyst is separated, and the residue can then be subjected to activated carbon treatment and ion-exchange resin treatment and concentrated into a concentration of 50% by mass to make a sugar solution of 250 g of sorbitol.

The cutting fluid and the smoothness improver for a cut surface of the present invention can be conveniently made by dissolving the present sugar alcohol in a solvent to obtain a sugar solution. The solvent is not particularly limited and for example, any of water such as ultrapure water, ion-exchange water, distilled water or tap water, an organic solvent and an industrial oil can be used. Alternatively, the present sugar alcohol in a liquid form may be used directly as the cutting fluid and the smoothness improver for a cut surface of the present invention.

The concentration of the present sugar alcohol in the sugar solution can be preferably equal to or higher than predetermined % by mass, for example, 35% by mass or higher, preferably 36% by mass or higher, more preferably 37% by mass or higher, further preferably 38% by mass or higher, still further preferably 39 to 70% by mass, from the viewpoint of an effect of improving the smoothness of a cut surface and an effect of reducing chipping.

In this context, the “sugar solution” according to the present invention refers to a solution containing the sugar alcohol as a solute. Specifically, the sugar solution may contain an additional component as long as the sugar solution contains the sugar alcohol as a solute. Examples of the additional component can include substances that are generally added to cutting fluids according to the type of a workpiece material or a process of cutting work. Examples thereof can include: oil agents such as plant oil, ester oil and polyether; extreme-pressure additives such as chlorinated paraffin and sulfurized fat and oil; ionic or nonionic surfactants; rust preventives such as carboxylate and organic amine; antifoaming agents such as fatty acid ester; antiseptics; and copper alloy corrosion inhibitors.

The viscosity of the sugar solution is, as shown in Example 3 mentioned later, preferably 9.7 mPa·s or more, more preferably 9.7 mPa·s or more and less than 376 mPa·s, further preferably more than 9.7 mPa·s and less than 376 mPa·s, still further preferably 20 mPa·s or more and less than 376 mPa·s, from the viewpoint of an effect of improving the smoothness of a cut surface. The viscosity is preferably 198 mPa·s or less from the viewpoint of basic performance as a cutting fluid, such as reduction in friction during cutting and washing of scraps, and easy handling. The viscosity of the sugar solution can be measured at 25° C. at the number of revolutions of 200 rpm using a single-cylinder rotational viscometer (type B viscometer or Brookfield viscometer) and a sampler container (adaptor) and a cylinder (spindle) selected according to the expected viscosity.

Next, a method for using the present invention will be described. The present invention can be used according to the same or similar method known to those skilled in the art as that using a conventional cutting fluid. Specifically, cutting can be performed while the cutting fluid or the smoothness improver for a cut surface of the present invention is supplied to near a cutting point. In this context, the process of cutting work is not particularly limited, and, for example, turning (straight turning, shoulder milling, taper turning, cutting-off, spinning, boring, threading, etc.), milling (cam milling, face milling, etc.), or wire saw machining (fixed abrasive machining or loose abrasive machining) can be used. The present invention can be suitably used in fixed abrasive machining with a wire saw among these processes.

In the present invention, a subject to be cut (workpiece material) is not particularly limited. Examples of the workpiece material can include: metals such as steel, cast iron, aluminum, aluminum alloy, copper, and copper alloy; and ceramics such as glass, silicon, silicon carbide, gallium nitride, and sapphire.

Hereinafter, the cutting fluid, the cutting method, and the smoothness improver for a cut surface according to the present invention will be described with reference to each Example. However, the technical scope of the present invention is not limited by features shown by these Examples.

EXAMPLES

<Test Method>

Preparation of a cutting fluid, measurement of a viscosity, manufacture of a wafer, and evaluation thereof in the present Examples were performed by the following methods (1) to (7) unless otherwise specified.

(1) Preparation of cutting fluid Each commercially available sugar alcohol in a liquid state shown in Table 1 was used as a cutting fluid either directly (as a stock solution) or after being mixed with water to have a predetermined viscosity. The commercially available cutting fluid used was a glycol-based cutting fluid.

TABLE 1 Sugar composition (% by mass) Tetrasaccharide Solid or higher concentration Disaccharide Trisaccharide sugar (% by Product Main component Sorbitol alcohol alcohol alcohol mass) name Manufacturer Sorbitol 65~75 10~20 5~10 5~10 70 WETON B Food 99   0.6   0.1   0.3 70 Sorbitol S Science Co., 95 2 1 2 70 Sorbitol C Ltd. 85 6 3 6 70 Sorbitol F Highly saccharified 40~50 40~50 8~13 1~10 70 ESWEE600 reduced starch syrup Moderately saccharified  3~10 43~55 15~25  5~38 70 ESWEE57 reduced starch syrup Reduced maltose syrup  1~10 65~75 5~15 10~20  75 Malbit

(2) Measurement of Viscosity

The viscosities of a commercially available cutting fluid and sugar solutions were measured by placing 20 mL of a sample in a low-viscosity adaptor of “Brookfield rotational viscometer DV2T HB” and attaching thereto spindle ULA(0), followed by measurement at the number of revolutions of 200 rpm in a circulating thermostat of 25° C.

(3) Manufacture of Wafer

A workpiece material (soda lime glass or silicon) was sliced by fixed abrasive machining with a wire saw electrocoated with a diamond abrasive to manufacture a wafer. The machining conditions are given below. Also, a schematic diagram of the cutting machine is shown in FIG. 1.

<<Machining Conditions>>

Cutting machine: rocking vibration-assisted diamond wire saw, workpiece material: soda lime glass or silicon, workpiece material size: 100×25×10 mm, wire diameter: 0.14 mm, abrasive grain size: 10 to 20 μm, wire tension: 20 N, wire travelling speed: 300 m/min, wire length: 28 m, rocking angle: ±10 degrees, rocking frequency: 0.141 Hz.

(4) Evaluation of Smoothness of Cut Surface

For the smoothness of a soda lime glass wafer, a name plate with the letters “Kanazawa Institute of Technology” was placed at the rear of the wafer, and the degree of a transparent moiety in the cut surface (hereinafter, referred to as a “transparent part”) was visually observed and photographed. Also, the area of the transparent part was measured, and the ratio of the transparent part to the cut surface was calculated by area percentage and scored according to the evaluation classification given below. If necessary, magnifying observation was performed using a microscope.

<<Evaluation classification>>+++: 60% by area or more, ++: 60 to 30% by area, +: less than 30% by area, −: 0% by area.

(5) Evaluation of Brittle Fracture Area

In general, the following two types of fractures are known to occur during cutting:

Brittle fracture; which causes cracks on a cut surface resulting in a finish with poor smoothness but requires a short machining time. Ductile fracture; which causes fewer cracks on a cut surface resulting in a finish with high smoothness but requires a long machining time due to surface planing-like machining.

The brittle fracture has heretofore occurred typically under the machining conditions described in the present test method (3). Accordingly, the brittle fracture area of each wafer fabricated in the present Examples was measured by the following method.

As shown in FIG. 2, an evaluation range of 15 mm in total involving 7.5 mm each in the direction of cut and the direction opposite thereto from the center of the cut surface of the wafer was established. The evaluation range was divided into 3 parts at 5-mm intervals and designated as a first section, a second section and a third section toward the direction of cut. In each section, a measurement range of 0.88 mm×0.66 mm was established at a total of 3 sites involving 2 sites positioned 1 mm from both ends of the wafer and 1 site at the center (50 mm from the end of the wafer). The measurement range was observed under a microscope. A “rough portion on the surface” was regarded as a portion where brittle fracture occurred. Its area was measured, and a mean was calculated.

(6) Evaluation of Chipping

As shown in FIG. 3, the direction of cut of the wafer was defined as a chipping width, and a direction perpendicular to the direction of cut was defined as a chipping depth. Their respective lengths were measured and means and standard deviations were calculated. Also, the means were scored according to the following evaluation classification.

<<Evaluation Classification>>

Chipping depth; +: a largest value of less than 27 μm, −: a largest value of 27 μm or more.

Chipping width; +: a largest value of less than 190 μm, −: a largest value of 190 μm or more.

(7) Evaluation of Waviness

As shown in FIG. 4, a measurement range of 20 mm in total involving 10 mm each in the direction of cut and the direction opposite thereto from the center of the cut surface of the wafer was established at a total of 3 sites involving 2 sites positioned 1 mm from both ends of the wafer and 1 site at the center (50 mm from the end of the wafer). The surface waviness of the measurement range was measured using a surface roughness measuring machine surfcom 1500 (Tokyo Seimitsu Co., Ltd.). A mean and a standard deviation of a largest cross-sectional height (Wt) in a waviness curve was calculated.

<Example 1> Comparison with Commercially Available Cutting Fluid

Wafers were fabricated using soda lime glass as a workpiece material and a commercially available cutting fluid and a sugar solution composed mainly of sorbitol (product name “WETON”) as cutting fluids. The sugar solution of sorbitol was used directly.

(1) Smoothness of Cut Surface

Results of evaluating the smoothness of a cut surface as to the wafers fabricated in the present Example 1 are shown in FIG. 5. As shown in FIG. 5, the cut surface of the wafer fabricated using the commercially available cutting fluid was rough, was free from a transparent part, and rendered the rearward letters “Kanazawa Institute of Technology” rarely viewable. The score of the area ratio of the transparent part was “−”. By contrast, the cut surface of the wafer fabricated using the sugar solution of sorbitol was transparent overall and rendered the rearward letters “Kanazawa Institute of Technology” clearly viewable. The score of the area ratio of the transparent part was “+++”.

In short, in the case of using the sugar solution of sorbitol as a cutting fluid, the area of the transparent part in the cut surface of the wafer was remarkably large as compared with the case of using the commercially available cutting fluid. This result demonstrated that use of the sugar solution of sorbitol as a cutting fluid can improve the smoothness of a cut surface.

(2) Brittle Fracture Area

Results of evaluating a brittle fracture area as to the wafers fabricated in the present Example 1 are shown in FIG. 6. As shown in FIG. 6, the brittle fracture area was 0.58 mm² in all of the first section, the second section and the third section in the wafer fabricated using the commercially available cutting fluid. By contrast, the brittle fracture area was 0.01 mm² in the first section, 0.02 mm² in the second section, and 0.07 mm² in the third section in the wafer fabricated using the sugar solution of sorbitol. In short, in the case of using the sugar solution of sorbitol, the brittle fracture area of the wafer was remarkably small as compared with the case of using the commercially available cutting fluid.

As mentioned in the test method (5), the brittle fracture area serves as an index for the amount of cracks on a cut surface. A smaller value of this area means a larger ductile fracture area, fewer cracks on a cut surface and higher smoothness of the cut surface. Thus, this result demonstrated that use of the sugar solution of sorbitol as a cutting fluid can decrease cracks on a cut surface during cutting and improve smoothness, by mainly causing ductile fracture, in spite of a short machining time (which has heretofore been a machining time that typically causes brittle fracture).

(3) Chipping

Results of evaluating chipping as to the wafers fabricated in the present Example 1 are shown in FIG. 7. As shown in FIG. 7, the chipping depth was 28.2 μm as a mean and given a score of “−” in the case of using the commercially available cutting fluid, whereas the chipping depth was 25.1 μm as a mean and given a score of “+” in the case of using the sugar solution of sorbitol. The chipping width was 194.3 μm as a mean and given a score of “−” in the case of using the commercially available cutting fluid, whereas the chipping width was 161.8 μm as a mean and given a score of “+” in the case of using the sugar solution of sorbitol.

In short, in the case of using the sugar solution of sorbitol, both the chipping depth and width were small as compared with the case of using the commercially available cutting fluid. This result demonstrated that use of the sugar solution of sorbitol as a cutting fluid can reduce chipping.

<Example 2> Study on Type of Sugar Alcohol

Wafers were fabricated using soda lime glass as a workpiece material and a commercially available cutting fluid and sugar solutions of various sugar alcohols as cutting fluids. The sugar alcohols used were sugar solutions composed mainly of sorbitol (product name “sorbitol C” and “sorbitol F”), and sugar solutions of highly saccharified reduced starch syrup (product name “ESWEE 600”), moderately saccharified reduced starch syrup (product name “ESWEE 57”) and reduced maltose syrup (product name “Malbit”). Among them, the sugar solutions of sorbitol were used directly, and the sugar solutions of highly saccharified reduced starch syrup, moderately saccharified reduced starch syrup and reduced maltose syrup were used after being each diluted with water to adjust the viscosity to 155 mPa·s (solid concentration: 67% by mass, 61% by mass and 65% by mass, respectively).

(1) Smoothness of Cut Surface

Results of evaluating the smoothness of a cut surface as to the wafers fabricated in the present Example 2 are shown in FIG. 8. As shown in FIG. 8, the cut surface of the wafer fabricated using the commercially available cutting fluid was rough, was free from a transparent part, and rendered the rearward letters “Kanazawa Institute of Technology” rarely viewable. The score of the area ratio of the transparent part was “−”. By contrast, the cut surface of the wafer fabricated using the sugar solution of sorbitol, highly saccharified reduced starch syrup, moderately saccharified reduced starch syrup or reduced maltose syrup was transparent overall and rendered the rearward letters “Kanazawa Institute of Technology” clearly viewable. The score of the area ratio of the transparent part was “++” or “+++”.

In short, in the case of using the sugar solutions of sorbitol, highly saccharified reduced starch syrup, moderately saccharified reduced starch syrup and reduced maltose syrup, the area of the transparent part in the cut surface of the wafer was large as compared with the case of using the commercially available cutting fluid. This result demonstrated that use of the sugar solution containing any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup as a cutting fluid can improve the smoothness of a cut surface.

(2) Chipping

Results of evaluating chipping as to the wafers fabricated in the present Example 2 are shown in FIG. 9. The chipping was evaluated as to the case of using the commercially available cutting fluid and the sugar solutions of highly saccharified reduced starch syrup, moderately saccharified reduced starch syrup and reduced maltose syrup.

As shown in FIG. 9, the chipping depth was 28.2 μm as a mean and given a score of “−” in the case of using the commercially available cutting fluid, whereas the chipping depth was 26.9 μm as a mean and given a score of “+” in the case of using the highly saccharified reduced starch syrup, was 25.2 μm as a mean and given a score of “+” in the case of using the moderately saccharified reduced starch syrup, and was 30.9 μm as a mean and given a score of “−” in the case of using the reduced maltose syrup. In short, in the case of using the highly saccharified reduced starch syrup and the moderately saccharified reduced starch syrup, the chipping depth was small as compared with the case of using the commercially available cutting fluid.

The chipping width was 194.3 μm as a mean and given a score of “−” in the case of using the commercially available cutting fluid, whereas the chipping width was 194.6 μm as a mean and given a score of “−” in the case of using the highly saccharified reduced starch syrup, was 186.4 μm as a mean and given a score of “+” in the case of using the moderately saccharified reduced starch syrup, and was 219.0 μm as a mean and given a score of “−” in the case of using the reduced maltose syrup. In short, in the case of using the moderately saccharified reduced starch syrup, the chipping width was small as compared with the case of using the commercially available cutting fluid.

This result demonstrated that use of the sugar solution of moderately saccharified reduced starch syrup as a cutting fluid can remarkably reduce chipping.

<Example 3> Study on Viscosity of Cutting Fluid

Wafers were fabricated using soda lime glass as a workpiece material and a commercially available cutting fluid and sugar solutions of various sugar alcohols as cutting fluids. The sugar solutions of various sugar alcohols were used either directly or after being diluted with water to adjust the viscosity as shown in Table 2. The viscosity of the commercially available cutting fluid was measured and was consequently 4.01 mPa·s.

TABLE 2 Sugar composition (% by mass) Tetrasaccharide Solid or higher Viscosity concentration Disaccharide Trisaccharide sugar Product Main component (mPa · S) (% by mass) Sorbitol alcohol alcohol alcohol name Manufacturer Sorbitol 155 70 65~75 10~20 5~10 5~10 WETON B Food 50.4 63 Science Co., 23.3 58 Ltd. 3.1 35 9.7 50 99   0.6   0.1   0.3 Sorbitol S 107.7 70 32 63 95 2 1 2 Sorbitol C 20.7 58 Highly saccharified 198 70 40~50 40~50 8~13 1~10 ESWEE600 reduced starch syrup Moderately 376 70  3~10 43~55 15~25  5~38 ESWEE57 saccharified reduced Reduced maltose 155 65  1~10 65~75 5~15 10~20  Malbit syrup 4.67   32.5

(1) Smoothness of Cut Surface

The smoothness of a cut surface was evaluated as to the wafers fabricated in the present Example 3. The results obtained using the sugar solutions having a viscosity of 198 mPa·s or less and the commercially available cutting fluid are shown in FIG. 10.

First, the cut surface of the wafer fabricated using the sugar solution having a viscosity of 376 mPa·s was rough, was free from a transparent part, and rendered the rearward letters “Kanazawa Institute of Technology” rarely viewable, though the results are not shown.

On the other hand, as shown in FIG. 10, the cut surfaces of the wafer fabricated using the sugar solutions having viscosities of 198, 155 and 107.7 mPa·s respectively were transparent overall and rendered the rearward letters “Kanazawa Institute of Technology” clearly viewable. The score of the area ratio of the transparent part was “+++”.

The cut surfaces of the wafer fabricated using the sugar solutions having viscosities of 32.0 mPa·s and 20.7 mPa·s respectively were also transparent overall and rendered the rearward letters “Kanazawa Institute of Technology” clearly viewable. The score of the area ratio of the transparent part was “++”.

The cut surface of the wafer fabricated using the sugar solution having a viscosity of 9.7 mPa·s had an upper transparent part, but was free from a transparent part from the center toward a lower region, and the score of the area ratio of the transparent part was “+”.

By contrast, the cut surfaces of the wafer fabricated using the sugar solutions having a viscosities of 4.67 mPa·s and 3.1 mPa·s or the commercially available cutting fluid having a viscosity of 4.01 mPa·s respectively were rough, were free from a transparent part, and rendered the rearward letters “Kanazawa Institute of Technology” rarely viewable. The score of the area ratio of the transparent part was “−”.

In short, in the case of using the sugar solution having a viscosity of 9.7 mPa·s or more, the area of the transparent part in the cut surface of the wafer was remarkably large as compared with the case of using the sugar solution having a viscosity of less than 9.7 mPa·s and the commercially available cutting fluid. This result demonstrated that use of the sugar solution having a viscosity of 9.7 mPa·s or more as a cutting fluid can improve the smoothness of a cut surface.

In the case of using the sugar solution having a viscosity of 9.7 mPa·s or more and less than 376 mPa·s, the area of the transparent part in the cut surface of the wafer was remarkably large as compared with the case of using the sugar solution having a viscosity of 376 mPa·s, the sugar solution having a viscosity of less than 9.7 mPa·s, and the commercially available cutting fluid. This result demonstrated that use of the sugar solution having a viscosity of 9.7 mPa·s or more and less than 376 mPa·s as a cutting fluid can further improve the smoothness of a cut surface.

(2) Chipping

Results of evaluating chipping as to the wafers fabricated in the present Example 3 are shown in FIG. 11. The chipping was evaluated as to the case of using the commercially available cutting fluid and the sugar solutions of sorbitol (product name “Sorbitol C”) having viscosities of 107.7, 32.0 and 20.7 mPa·s.

As shown in FIG. 11, the chipping depth was 28.2 μm as a mean and given a score of “−” in the case of using the commercially available cutting fluid, whereas the chipping depth was 20.9 μm as a mean and given a score of “+” in the case of using the sugar solution having a viscosity of 107.7 mPa·s, was 24.5 μm as a mean and given a score of “+” in the case of using the sugar solution having a viscosity of 32.0 mPa·s, and was 26.3 μm as a mean and given a score of “+” in the case of using the sugar solution having a viscosity of 20.7 mPa·s. The chipping width was 194.3 μm as a mean and given a score of “−” in the case of using the commercially available cutting fluid, whereas the chipping width was 166.6 μm as a mean and given a score of “+” in the case of using the sugar solution having a viscosity of 107.7 mPa·s, was 177.2 μm as a mean and given a score of “+” in the case of using the sugar solution having a viscosity of 32.0 mPa·s, and was 187.6 μm as a mean and given a score of “+” in the case of using the sugar solution having a viscosity of 20.7 mPa·s.

In short, in the case of using the sugar solutions having viscosities of 107.7 mPa·s, 32.0 mPa·s and 20.7 mPa·s, the chipping width and the chipping width were small as compared with the case of using the commercially available cutting fluid, demonstrating that use of the sugar solution having a viscosity of 20.7 mPa·s or more and 107.7 mPa·s or less as a cutting fluid can reduce chipping. This result, together with the result of the present Example 3(1), demonstrated that use of the sugar solution having a viscosity of 9.7 mPa·s or more and less than 376 mPa·s as a cutting fluid can reduce chipping.

(3) Waviness

Results of evaluating waviness as to the wafers fabricated in the present Example 3 are shown in FIG. 12. The waviness was evaluated as to the case of using sugar solutions of sorbitol (product name “WETON”) having viscosities of 155, 50.4 and 23.3 mPa·s.

As shown in FIG. 12, the mean of largest cross-sectional height (Wt) in the waviness curve was 39.5 μm in the sugar solution having a viscosity of 155 mPa·s, 43.7 μm in the sugar solution having a viscosity of 50.4 mPa·s, and 29.0 μm in the sugar solution having a viscosity of 23.3 mPa·s. In short, this result demonstrated that use of the sugar solution having a viscosity of 23.3 mPa·s or more and 155 mPa·s or less as a cutting fluid suppresses waviness within a predetermined range. This result, together with the result of the present Example 3(1), demonstrated that use of the sugar solution having a viscosity of 9.7 mPa·s or more and less than 376 mPa·s as a cutting fluid suppresses waviness within a predetermined range.

<Example 4> Evaluation of Cutting Fluid for Silicon

A wafer was fabricated using silicon as a workpiece material and a commercially available sugar solution of sorbitol (product name “Sorbitol F”) directly as a cutting fluid. Subsequently, the cut surface of the fabricated silicon wafer was visually observed and photographed. The results are shown in FIG. 13.

As shown by the arrow in the circled portion in FIG. 13, the cut surface of the silicon wafer was so remarkably smooth that a finger put above the silicon wafer was reflected in the cut surface. This result demonstrated that use of the sugar solution of sorbitol as a cutting fluid can improve smoothness in such a way that the cut surface of silicon is rendered mirror-smooth. 

1-5. (canceled)
 6. A cutting method having a step of cutting a workpiece material by fixed abrasive machining with a wire saw using, as a cutting fluid, a sugar solution containing any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup.
 7. A cutting method having the step of cutting a workpiece material using, as a cutting fluid, a sugar solution containing any sugar alcohol selected from sorbitol, reduced starch syrup and reduced maltose syrup and having said sugar alcohol concentration of 35% by mass or higher.
 8. The cutting method according to claim 7, wherein said sugar alcohol concentration in said sugar solution is 50% by mass or higher. 